Such a knife is known from DE 197 23 279 [U.S. Pat. No. 6,148,520]. The knife has a housing in which a blade support can move between a safety position and a cutting position. In the safety position, the blade is retracted into the housing and cannot be touched by the user of the knife. In the cutting position, the blade projects out of an opening of the housing. The blade support can be moved by an actuator from the safety position into a first cutting position. A cutting force acting on the blade can shift the blade support from the first cutting position into a second cutting position. The second cutting position differs from the first cutting position in that the blade support can move back into the safety position even if the actuator is in the actuating position. In contrast, in the first cutting position with the actuator actuated, the blade support cannot move back into the housing.
In DE 10 2008 019 441 [US 2009/0260235], a knife is disclosed in which a lever is pivoted on the blade support and the actuator. By moving an actuator into an actuating position, the blade support can be moved from a safety position into a first cutting position. In the first cutting position, a support element fastened to the lever is supported on the housing. Moving the blade support from the first cutting position into the second cutting position, causes the support element to lose contact with the housing and the blade support can move back into the safety position even if the actuator is in the actuating position.